Elastomeric sheets, membranes and films are used in a variety of applications such as roofing, geo membranes, and pond liners. In the past, polymeric roof sheeting materials in the form of single-ply roofing membranes have been used to cover flat rooftops typically found on industrial or commercial buildings, e.g., factories, hospitals, and school buildings. Owing to the combination of low cost, ease of installation, weather resistance, and good physical properties, ethylene-propylene-(optional)diene terpolymer based compounds [“EP(D)M”] have been used in single-ply thermoset roof membrane formulations. When roof membranes are used to cover a large industrial roof, the ends of the sheets are typically spliced together to form a structurally rigid seam. However, after installation, this seam is constantly subjected to adverse weather conditions, such as thermal stresses, high velocity winds, and moisture. The structural integrity of the seam is an important consideration during installation.
Elastomeric compounds based on EP(D)M polymers need to possess the right combination of processability and physical properties both in the vulcanized and unvulcanized state to satisfy manufacturing and end use application requirements. From a manufacturing standpoint, two noteworthy properties that need to be optimized in the unvulcanized formulation are compound tack and green strength. The uncured elastomeric sheets coming off the calendar roll should possess adequate tack to permit splicing of individual sheets to form a sheet that is several times larger than the calendered sheet in width. The unvulcanized compound should also have adequate green strength to be rolled onto a mandrel without sagging. Tack and green strength are influenced by polymer crystallinity. Tack demands either absence or lower crystallinity while green strength demands higher crystallinity. Design of a single EP(D)M polymer that has these contrasting polymer features to meet the tack and green strength requirements is a synthetic challenge.
Roofing membranes made from physically blended EP(D)M polymers are known. For example, U.S. Pat. No. 5,468,550 describes EP(D)M based roof sheet materials, including physical blends. U.S. Pat. No. 5,654,370 also describes membranes made from physically blended EP(D)M polymers. The present invention provides improved tack and green strength as well as other benefits of blended materials without having to physically mix the polymers.
For additional background, see also U.S. Pat. Nos. 5,854,327, 5,888,602, 5,859,114, 5,582,890, 5,389,715, 5,286,798, 5,370,755, 5,256,228, 5,242,970, 5,700,538, 5,571,868, and 4,722,971; WO 98/02471, WO 99/45046, WO 99/45047, and WO 99/45049; and U.S. application Ser. No. 09/570,969, 60/258,096, and 60/258,131.